Mechanical jack

ABSTRACT

Jack comprises ground engaging base, upright hollow tubular support post on base, load carrying column slidable in post, and linkages and latches to raise column. Interchangeable heads mounted on top of column are shaped and arranged for different loading conditions. An actuating lever is pivotally mounted on a fulcrum fixedly attached to the post and has a long manual operating arm and a short, forked actuating arm extending in the opposite direction. Tension links pivoted at their upper ends to the free ends of the forks carry latch pins at their lower ends spring biased to enter axial slots at opposite sides of the post and engage selected apertures axially spaced in columns. Lowering operating arm raises links, pins, and column. Lock pin passed through higher apertures in column rests on top of post to support load, and latch pins may be lowered to engage new apertures for successive lifting stages.

United States Patent [1 1 Johnson 111 3,749,361 1 July 31,1973

1 1 MECHANICAL JACK [22] Filed: Mar. 1, 1972 [21] Appl. No.: 230,646

[52] U.S. Cl. 254/2 R, 254/8 R, 254/105, 254/118 [51] Int. Cl. 860p 1/00, B66f 1/04, B66f 3/00 [58] Fleld of Search 254/2 R, 2 B, 2 C, 254/113-118, 105-111; 248/354 P [56] References Cited UNITED STATES PATENTS 371,887 10/1887 Hitt 254/114 517,465 4/1894 Lewis 254/118 573,950 12/1896 Woodward... 254/118 507,038 10/1893 Raby 254/118 614,777 11/1898 Stoddard 254/116 1,014,801 1/1912 Beard 254/116 2,786,650 3/1957 Bottorff 254/105 Primary Examiner-Othell M. Simpson Attorney-Forrest J. Lilly I 57] ABSTRACT Jack comprises ground engaging base, upright hollow tubular support post on base, load carrying column slidable in post, and linkages and latches to raise column. Interchangeable heads mounted on top of column are shaped and arranged for different loading conditions. An actuating lever is pivotally mounted on a fulcrum fixedly attached to the post and has a long manual operating arm and a short, forked actuating arm extending in the opposite direction. Tension links pivoted at their upper ends to the free ends of the forks carry latch pins at their lower ends spring biased to enter axial slots at opposite sides of the post and engage selected apertures axially spaced in columns. Lowering operating arm raises links, pins, and column. Lock pin passed through higher apertures in column rests on top of post to support load,'and latch pins may belovvei'ed to engage new apertures for successive lifting stages.

21 Claims, 12 Drawing Figures PAIENIE JUl. 3 1 ms SHEET 2 0F 2 MECHANICAL JACK BACKGROUND OF THE INVENTION This invention lies in the general field of manually operated mechanical lifting jacks for raising and supporting loads at predetermined levels about a supporting surface. It is particularly directed to a jack of such type which is especially suited for use with airplanes, although well adapted for automobile use, and which is relatively light, sturdy, and stable and requires minimum storage space. y

In the course of performing maintenance, service, or repair work on airplanes, it is often necessary or desirable to raise all or part of an airplane about its normal ground supported level and to maintain it in raised position for some length of time. This may be done to provide convenient access to lower parts of the engine or structure or to raise one or more wheels off the ground to facilitate work on the landing gear.

An airplane of any type is normally designed to be as light as possible consistent with loading and perfor mance requirements, and its exterior surfaces are capable of sustaining only distributed loads. Therefore, the structure is usually reinforced at a few selected points, and lifting or jack pads are provided at these points for engagement by ground supported jacks. These jack pads may be at the undersides of the fuselage or wings, and the location and spacing between them varies widely from one make to another.

The commercial airplanes operated by airlines are usually maintained in their own shops and specific equipment is usually built for each type. However, the service facilities which handle small executive and pleasure type airplanes must be able to handle many kinds with minimum equipment. Thus there is a need for jacking equipment which is universally usable with all types to avoid duplication. The equipment must be light and simpleyet extremely durable and preferably should be foldable or separable for compact storage.

SUMMARY OF THE INVENTION.

The present invention provides avery satisfactory an swer to this need and offers a jack which is simple in construction and operation and which may be operated in substantially the same way with any type of airplane.

A few simple accessories'adap't it to high and low wing strength with minimum weight. The wall of the column is pierced with two series of axially spaced apertures, the two series being diametrically opposed, and cooperating apertures being in diametral registry to receive a lock pin and latch pins.

The post is provided with a pair of diametrically opposed slots which register with the apertures. A fulcrum is fixedly mounted on the post, preferably near the top, and an actuating lever is pivotally mounted on the fulcrum. The lever includes a manual operatingarm extending away from the post and a forked actuating arm, the forks extending to each side of the post. Atension link is pivotally connected at its upper end to the free end of each fork, and a latch pin is connected to the lower end of each link and spring biased to extend inward through the slot and into engagement with a selected aperture. The latch pins are so shaped that they positively engage the apertures during upward movement and are cammed out of the apertures during downward movement.

To accomplish raising of the column, the operating lever is first raised to lower the latch pins to the lowest available aperture and is then lowered to raise the latch pins and the column. The lever and links are so dimensioned that when the operating arm is in its lowermost position the longitudinal axis of each link has passed over-center with respect to the fulcrum pivot and the lever is self-locking. A lock pin is now passed through a pair of registered apertures in the column just above the top of the post as a safeguard against accidental lowering. To increase the total height of the jackby another increment, the operating arm is again raised and the lock pin rests on the top of the post to transmit the total load from the column to the post. Continued raising of the operating arm lowers the latch pins to the lowest available apertures and they are then raised again to move the column upward and lock it as before. This step may be repeated several times if necessary.

To lower the column, the latch pins are manually moved out of the apertures which they are engaging at the time and moved to the uppermost available apertures. They are then raised slightly to release the lock pin, and the load is lowered by raising the operating arm. This sequence is repeated until the jack is free of the load. Various accessories make it possible to engage the wing, landing gear, or propeller of the air- BRIEF DESCRIPTION OF THE DRAWINGS Various other advantages and features of novelty will become apparent as the description proceeds in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic view in perspective of the jack of the invention applied to an airplane;

FIG. 2 is a perspective view of an auxiliary head adapted to engage a jack pad;

FIG. 3 is a schematic view illustrating the application of the head of FIG. 2;

FIG. 4 is a schematic elevational view of a second auxiliary head adapted to engage an airplane propeller;

FIG. 5 is a schematic side elevational view of the jack with a head and other accessories for use in raising an automobile;

FIG. 6 is a perspective view ofthe head of FIG. 5;

FIG. 7 is a perspective view of the bumper hook of FIG. 5;

FIG. 8- is a schematic side elevational view of the main elements of the jack and the lifting linkage;

FIG. 9 is a-view taken on the line 9-9 of FIG. 8;

FIG. 10 is a vertical sectional view through the main elements of the jack and the linkage;

FIG. 11 is a sectional view taken on line 11-11 of FIG. 8', and 7 FIG. 12 is a schematic view in perspective of the main elements of the jack and cooperating components.

DESCRIPTION OF PREFERRED EMBODIMENTS The general arrangement illustrated in FIG. I shows a basic unit 10- comprising an elongate base 12, a hollow tubular support post 14, and a hollow tubular column 16 slidably mounted in the post, the tip 18 of the upper end serving as a load supporting head. Linkage 20 raises and lowers the column with respect to the post and maintains it in elevated position by overcenter locking action. The base includes an elongate tubular main body 22, a frictional ground engaging foot 24 on the rear portion, a short lateral bearing 26 at the forward portion, an axle 28 laterally slidable in the bearing, and wheels or rollers 30 rotatably mounted on the ends of the axle. A short upright socket 32 receives and supports post 14 for rotation about its own axis.

The mechanism for raising and lowering the column with respect to the post is shown in greater detail in FIGS. 8 to 10, where it will be seen that the column 16 is provided with a row or series of axially spaced recesses in the form of holes or apertures 34 through its wall at two opposite loci, each pair of cooperating apertures being in diametral registry and the rows extending throughout the major portion of the length of the column. The post is provided with a pair of relatively short slots 36 passing through diametrically opposite portions of its wall in registry with the apertures.

A fulcrum 38 is welded or otherwise secured to the wall of the post near its upper end and comprises spaced ears 40 with aligned pivot holes 42 on an axis transverse to the axis of the post. An actuating lever 44 is pivotally mounted on the fulcrum by means of pivot pin 46 extending through holes 42 and includes a manual operating arm 48 extending away from the post and an actuating arm having forks 50 passing to each side of the post. A tension link 52 is pivotally connected at its upper end to the free end of each of the actuating forks or arms 50 by means ofa pivot shaft 54. The links are biased toward the post by springs 56 mounted on the pivot shaft and retained by nuts 58.

The lower end of each link carries a latch pin 60 which is biased by the spring loading on the arm to extend through slot 36 and into a registering recess or aperture 34. The upper surface 62 of the inner end of each pin is perpendicular to the axis of the post while the lower surface 64 is chamfered as shown to form a cam surface. To raise the column with respect to the post, the operating arm is raised to its uppermost position as indicated in broken lines, which lowers the latch pins to the lowest available aperture 34. As the links and pins move downward the chamfered surfaces 64 engage the lower margins of the apertures and are cammed out of engagement. The arm 48 is now lowered to the solid line position, raising arms 50, links 52 and pins 60. Since surfaces 62 of the pins positively engage the upper margins of the apertures, they will raise the column. It will be noted that the geometry of the parts is so chosen that after a small initial movement the mechanical advantage of the lever gradually increases substantially to infinity, and when arm 48 reaches its lowermost position the longitudinal axis 66 of link 52 passes over the axis of pivot pin 46 and the lever becomes self locking to sustain the load without being held.

In this position, one of the apertures 34 is just above the saddle-like recess 68 in the upper edge of the post. An identical recess is formed at the diametrically opposite side. A lock pin 70 is now passed through the two recesses and arm 48 is raised a short distance,lowering the column to cause the lock pin to seat in recesses 68 and transmit the load from the column to the post.

Thus the lock pin serves the dual purpose of a safety lock when arm 48 is in self-locking position and as the load transmitter when arm 48 is raised. If the single movement or sequence just described does not raise the load as high as desired it may be repeated one or more times. Since the lock pin will transfer the load, arm 48 may be raised safely to lower the latch pins to any desired successive aperture as indicated in FIG. 10. The pins and the column are then raised and lock pin 70 is moved to its new safety position.

Substantially the reverse procedure is followed to lower an elevated load. With the lock pin in support engagement with the post, latch pins 60 are manually moved out of the recesses which they occupy at the moment and arm 48 is lowered to raise pins 60 to the height of the highest available recesses where they are allowed to enter such recesses in response to the spring bias. Arm 48 is then pushed down to over-center position, unloading lock pin 70 which is withdrawn and moved to a higher position such as shown in FIG. 8. Arm 48 is now raised to lower the latch pins and column until lock pin 70 again engages recesses 68. This procedure may be repeated until the jack is free of the load.

It is also possible and frequently desirable to lower the load and release the jack in one swinging motion. A long extension handle 72 is fitted into the aft end of main body 22 as illustrated in FIG. 1. By pulling rearward and upward on the handle, the base is moved rearward on rollers 30 and tilted about the point of load application to swing it out from under the vertical projection of the load point. The jack can also be moved into load supporting position by a reverse procedure. The height of the load head is first adjusted to such a level as will raise the load to some extent and it is then swung from the broken line to the solid line position of FIG. 1. If greater elevation is then desired, the jacking procedure previously described may then be followed.

The auxiliary head 74 shown in FIG. 1 is illustrated in greater detail in FIGS. 2 and 3, where it will be seen that it includes a stub shaft 76 to be inserted in the head of the column, a clevis 78, and a load block 80 pivotally mounted in the clevis by pins 82 and having a generally planar upper surface with a recess 84 to engage boss 86 of the lifting or jack pad 88 mounted on the under surface of wing 90. As indicated in FIG. 3, the pivotal mounting of the load block enables it to be fully engaged with the jack pad while column 16 is tilted in preparation for the raising operation.

In some cases it is desirable to lift the nose of an aircraft by means of the propeller. For this purpose, the auxiliary head 92 of FIG. 4 includes a stub shaft 94 fitting into the head of column 16, a cross bar 96 attached to the stub shaft, and a pair of upwardly concave sad dles 98 attached to the ends of the cross bar by short vertical posts 100. The saddles engage the blades of propeller 102 at points equidistant from the axis of the hub.

The jack of this invention is also readily adaptable for use in automobile repair shops, providing rapid action and reliable support. As illustrated in FIGS. 5, 6, and 7, an auxiliary head 104 has a stub shaft 106 and an upstanding flange 108 having a notch 110 formed in its upper edge to receive and retain a link of a chain 112. A pair of hooks I14 are fixed to a cross bar 116 seated in the fold of a flexible strap 118 which in turn is attached to an end of chain 112. As shown in FIG. 5, the

hooks securely engage the lower edge of an automobile bumper 120 while the strap 118 contacts the front face of the bumper without scratching it, and chain 112 is pulled tautand one of its links engaged with notch 110. Raising and lowering are accomplished in the same way as previously described. Again, it will be apparent that the initial height of the jack may be adjusted to be suitable for practically all automobiles and the raising and lowering of the load accomplished by tilting the jack. The same accessory may be used in most cases for engaging an airplane landing gear strut for work on landing gear components. ln either case it will be seen that the loading is applied vertically and well within the area between the rollers 30 and the foot 24 so that the support is always stable and safe.

Since post 14 is rotatably mounted in socket 32, the post and column may be readily adjusted angularly to engage the load. it is also important to be able to locate the post and column close to the vertical line of the load even though there may be obstacles on the ground such as an airplane wheel or the like. Since bearing 26 is only about as wide as the main body and axle 28 is slidable in the bearing, it is possible to offset the rollers so that one of them is adjacent to the main body, thus making it possible to provide lift immediately adjacent to the obstacle. When the jack is to be applied to high wing airplanes, an extension shaft of any desired length may be mounted in the top of the column.

It will be noted that the jack of this invention is not fully automatic but requires various manual operations. The reason is that it is intended to be as simple and sturdy as possible while still accomplishing all of its intended functions, and also to be relatively economical to manufacture. The additional features shown in FIGS. 11 and 12 make the jack more automatic and also prevent accidental disengagement of the latch pins from the guide slots.

A guard collar 122 is freely slidably mounted on post 14 below the latch pins 60 and is provided with diametrically opposed strips 124 having upstanding ears 126 in which apertures 128 are formed to slidingly receive the extended shanks of latch pins 60. The cars are located a predetermined distance radially outward of the post to engage the lower ends of links 52, which are fixedly connectedto latch pins 60, and limit the outward movement of the links to such an extent that the latch pins will cleanly disengage from apertures 34 but remain in guide slots 36 for axial movement to a new location. Instead of using springs 56 at the pivotal connection of links 52 to their actuating arms, a conical spring 130 may be located on each latch pin 60 extension between the link and ear 126 to urge the links and pinsradially inward. Because of its conical form it may be compressed to a flat spiral occupying minimum space and minimizing the needed radial extent of the ears.

To move the links and latch pins outward against the spring bias, a second collar 132 is freely slidably and rotatably mounted on post 14 above the latch pins. The collar is provided with a pair of diametrically opposed cams 134 which move into contact with the inner surfaces of the links as the collar is rotated and move them out sufficiently to cause the inner ends of the latch pins to disengage from apertures 34. Stops 136 may be provided to limit the cam movement so that the links will rest on the high points. Rotation of the cam collar is facilitated by the provision of pins or handles 138. The

camming operation is utilized when it is desired to raise the latch pins without also raising the column, such as during the load lowering operation previously described. Since the collar is freely rotatable it is desir-, able to provide means for preventing unintended rotation which might cam the latch pins out of engagement when such action is not desired. For this purpose a notch 140 is formed in the lower edge of the collar at opposite points to engage the latch pins. The notches are so located that when they are in locking engagement the cam surfaces are in non-lifting positions with respect to the links.

It will be apparent that the invention disclosed herein provides a versatile, rugged jack which is simple in construction and operation and is readily adaptable to a wide variety of load lifting situations.

I claim:

1. A mechanical jack comprising:

a ground engaging base;

a hollow tubular support post mounted on the base in upright position;

an axially elongate guide slot extending through the wall of the post;

a load carrying column slidably mounted in the post to raise and lower a load and having a load engaging head at its upper end;

a series of axially spaced recesses in the wall of the column'for engagement by a lock pin and a latch p a fulcrum fixedly mounted on the post;

an actuating lever pivotally mounted on the fulcrum for swinging about an axis transverse to the axis of the post and having a manual operating arm and an actuating arm extending in opposite directions from the pivotal axis;

a tension link pivotally connected at its upper end to the free end of the actuating arm and having a latch pin at its lower end resiliently biased to extend'radially through the guide slot and engage one of the recesses in the column;

and a removable lock pin to engage an upper portion of the post and an adjacent recess in the column to retain the column at a selected elevation with respect to the post;

the inner end of the latch pin being formed to positively engage a recess during rising movement of thepin and to be urged out of engagement bya recess margin vduringdescending movement of the pin.

v 2.- A jack as claimed in claim 1 in which the lock pin engaged in the recess rests on the upper end of the post to transmit the load from the column to the post.

3. A jack as claimed in claim 2;

in which the recesses are apertures extending diametrically through the column, and the lock pin is elongate and extends entirely through the column with its ends'projecting to rest on the upper end of the post at diametrically opposite points.

4. A jack as claimed in claim 3;

and saddle shaped recesses formed in the upper edge of the post at diametrically opposite points to receive the projecting ends of the lock pin and prevent rotation of the column with respect to the post.

5. A jack as claimed in claim 3;

the column being a hollow tube, and the recesses being apertures in the wall of the tube at diametrically opposite points to define a diametral passage.

6. A jack as claimed in claim 1;

the link and actuating lever being so dimensioned and located that when the link is at the low point of its travel the pivotal connection of the link to the actuating arm is substantially directly vertically above the point of connection of the link to the latch pin and laterally adjacent to the fulcrum pivot actuating lever;

the lowering of the manual operating arm serving to raise the actuating arm with gradually increasing mechanical advantage to a final position in which the central longitudinal axis of the link is over center with respect to the fulcrum pivot to make the operating arm self-locking in its lowermost position.

7. A jack as claimed in claim 1;

the base including an elongate main body having frictional ground engaging means at a rear portion and an axle bearing at a forward portion with its axis extending laterally of the axis of the main body and being short in the direction of its axis;

an axle slidable in the bearing and carrying a ground engaging roller at each end;

the axle being considerably longer than the bearing to enable it to slide laterally and locate the main body close to a selected wheel to improve access in crowded locations.

8. A jack as claimed in claim 1;

the post being rotatably mounted on the base for rotation about its own longitudinal axis for angular adjustment to the position of the load.

9. A jack as claimed in claim 1;

and an auxiliary head located on the top of the column;

the auxiliary head including a tiltably mounted load block with a generally planar upper surface;

and a recess in the upper surface to engage a lifting pad on an aircraft wing.

10. A jack as claimed in claim 1;

and an auxiliary head located on the top of the column;

the auxiliary head having an elongate horizontal cross arm;

and anupwardly concave saddle at each end of the cross arm to engage a horizontal propeller for lifting an aircraft.

11. A jack as claimed in claim 1;

and an auxiliary head located on the top of the column;

the auxiliary head having an upstanding flange with a notch in its upper edge to receive and retain a link of a chain;

a hook formed to engage the lower edge of an automobile bumper;

a flexible strap attached to the hook;

and an elongate chain attached to the strap and adapted to be engaged with the flange by a selected link to transfer the load of the automobile to the jack.

12. A jack as claimed in claim 1;

including a second guide slot in the wall of the post parallel to and diametrically opposed to the first slot;

a second series of recesses in the wall of the post parallel to and diametrically opposed to the first series;

a second actuator arm parallel to the first arm and laterally spaced therefrom, with the arms extending on opposite sides of the post;

a second tension link pivotally connected to the free end of the second actuator arm;

and a second latch pin connected to the lower end of the second link and resiliently biased to extend radially through the second guide slot and engage one of the recesses in the second series;

the opposed positions of the latch pins serving to centralize the loading of the column on the post.

13. A jack as claimed in claim 12;

the links being loosely mounted on their pivotal connections to the actuating arms;

and springs engaging said links to urge their lower ends toward the post and cause the latch pins to move radially inward into engagement with the recesses.

14. A jack as claimed in claim 12;

the inner ends of the latch pins having upper surfaces which are perpendicular to the axis of the post for positive engagement with the upper margins of the recesses during upward movement of the pins;

the lower surfaces of the inner ends being chamfered to serve as cams for engaging the lower margins of the recess and urging the pins radially outward during downward movement of the pins.

15. A jack as claimed in claim 12;

in which the column is a hollow tube and the recesses are apertures through the wall of the tube and arranged in diametrically opposed relation to define diametral passages through the column.

16. A jack as claimed in claim 1;

and a collar rotatably mounted on the post above the latch pin;

and a cam surface on the collar rotatable with the collar to engage the lower end of the link and move it outward to cause the attached latch pin to move out of engagement with a recess.

17. A jack as claimed in claim 16;

and a notch in the lower edge of the collar engageable with the latch pin to prevent rotation of the collar;

the notch being so located that when it is in locking engagement the cam surface is in non-lifting position with respect to the link.

18. A jack as claimed in claim 1;

and a collar slidably mounted on the post below the latch pin;

an ear extending upward from the collar and formed with an aperture to slidingly receive the outer portion of the latch pin;

the ear being located radially outward of the post a predetermined distance to limit outward movement of the link and disengagement of the latch pin from the slot.

19. A jack as claimed in claim 18;

and a coil spring surrounding the latch pin between the earand the link to resiliently urge the link inward toward the post and cause the pin to enter the recess.

20. A mechanical jackcomprising:

a ground engaging base;

a hollow tubular support post mounted on the base in upright position;

a pair of axially elongate guide slots extending through the wall of the post and arranged in parallel diametrically opposed relation;

a hollow tubular load carrying column axially slidably mounted in the post to raise and lower a load and having a load engaging head at its upper end;

two series of axially spaced apertures extending through the wall of the column for engagement by a lock pin and a latch pin, the two series being diametrically opposed and associated pairs of apertures being diametrically in register to define diametral passages through the column;

a fulcrum fixedly mounted on the post;

an actuating lever pivotally mounted on the fulcrum for swinging about an axis transverse to the axis of the post and having a manual operating arm extending in a direction away from the post and a pair of actuating arms in parallel spaced relation and extending toward the post and passing on each side thereof;

a pair of tension links, each pivotally connected at its upper end to the free end of one of the actuating arms and having a latch pin at its lower end resiliently biased to extend radially through one of the guide slots and into one of the apertures in the column;

and a removable lock pin to engage an upper portion of the post and pass through an associated pair of apertures in the column to retain the column at a selected elevation with respect to the post;

the inner ends of the latch pins being formed to positively engage the upper margins of associated apertures during upward movement of the pins and to be urged out of engagement by contact with lower margins of associated apertures during downward movement of the pins.

21. A jack as claimed in claim 20;

in which the lock pin projects out of the apertures at both sides of the column with its ends resting on the upper end of the post at diametrically opposite points to transmit the load from the column to the post. 

1. A mechanical jack comprising: a ground engaging base; a hollow tubular support post mounted on the base in upright position; an axially elongate guide slot extending through the wall of the post; a load carrying column slidably mounted in the post to raise and lower a load and having a load engaging head at its upper end; a series of axially Spaced recesses in the wall of the column for engagement by a lock pin and a latch pin; a fulcrum fixedly mounted on the post; an actuating lever pivotally mounted on the fulcrum for swinging about an axis transverse to the axis of the post and having a manual operating arm and an actuating arm extending in opposite directions from the pivotal axis; a tension link pivotally connected at its upper end to the free end of the actuating arm and having a latch pin at its lower end resiliently biased to extend radially through the guide slot and engage one of the recesses in the column; and a removable lock pin to engage an upper portion of the post and an adjacent recess in the column to retain the column at a selected elevation with respect to the post; the inner end of the latch pin being formed to positively engage a recess during rising movement of the pin and to be urged out of engagement by a recess margin during descending movement of the pin.
 2. A jack as claimed in claim 1; in which the lock pin engaged in the recess rests on the upper end of the post to transmit the load from the column to the post.
 3. A jack as claimed in claim 2; in which the recesses are apertures extending diametrically through the column, and the lock pin is elongate and extends entirely through the column with its ends projecting to rest on the upper end of the post at diametrically opposite points.
 4. A jack as claimed in claim 3; and saddle shaped recesses formed in the upper edge of the post at diametrically opposite points to receive the projecting ends of the lock pin and prevent rotation of the column with respect to the post.
 5. A jack as claimed in claim 3; the column being a hollow tube, and the recesses being apertures in the wall of the tube at diametrically opposite points to define a diametral passage.
 6. A jack as claimed in claim 1; the link and actuating lever being so dimensioned and located that when the link is at the low point of its travel the pivotal connection of the link to the actuating arm is substantially directly vertically above the point of connection of the link to the latch pin and laterally adjacent to the fulcrum pivot actuating lever; the lowering of the manual operating arm serving to raise the actuating arm with gradually increasing mechanical advantage to a final position in which the central longitudinal axis of the link is over-center with respect to the fulcrum pivot to make the operating arm self-locking in its lowermost position.
 7. A jack as claimed in claim 1; the base including an elongate main body having frictional ground engaging means at a rear portion and an axle bearing at a forward portion with its axis extending laterally of the axis of the main body and being short in the direction of its axis; an axle slidable in the bearing and carrying a ground engaging roller at each end; the axle being considerably longer than the bearing to enable it to slide laterally and locate the main body close to a selected wheel to improve access in crowded locations.
 8. A jack as claimed in claim 1; the post being rotatably mounted on the base for rotation about its own longitudinal axis for angular adjustment to the position of the load.
 9. A jack as claimed in claim 1; and an auxiliary head located on the top of the column; the auxiliary head including a tiltably mounted load block with a generally planar upper surface; and a recess in the upper surface to engage a lifting pad on an aircraft wing.
 10. A jack as claimed in claim 1; and an auxiliary head located on the top of the column; the auxiliary head having an elongate horizontal cross arm; and an upwardly concave saddle at each end of the cross arm to engage a horizontal propeller for lifting an aircraft.
 11. A jack as claimed in claim 1; and an auxiliary head located on the top of the column; the auxiliary head having an upstanding flange with a notch in its upper edge To receive and retain a link of a chain; a hook formed to engage the lower edge of an automobile bumper; a flexible strap attached to the hook; and an elongate chain attached to the strap and adapted to be engaged with the flange by a selected link to transfer the load of the automobile to the jack.
 12. A jack as claimed in claim 1; including a second guide slot in the wall of the post parallel to and diametrically opposed to the first slot; a second series of recesses in the wall of the post parallel to and diametrically opposed to the first series; a second actuator arm parallel to the first arm and laterally spaced therefrom, with the arms extending on opposite sides of the post; a second tension link pivotally connected to the free end of the second actuator arm; and a second latch pin connected to the lower end of the second link and resiliently biased to extend radially through the second guide slot and engage one of the recesses in the second series; the opposed positions of the latch pins serving to centralize the loading of the column on the post.
 13. A jack as claimed in claim 12; the links being loosely mounted on their pivotal connections to the actuating arms; and springs engaging said links to urge their lower ends toward the post and cause the latch pins to move radially inward into engagement with the recesses.
 14. A jack as claimed in claim 12; the inner ends of the latch pins having upper surfaces which are perpendicular to the axis of the post for positive engagement with the upper margins of the recesses during upward movement of the pins; the lower surfaces of the inner ends being chamfered to serve as cams for engaging the lower margins of the recess and urging the pins radially outward during downward movement of the pins.
 15. A jack as claimed in claim 12; in which the column is a hollow tube and the recesses are apertures through the wall of the tube and arranged in diametrically opposed relation to define diametral passages through the column.
 16. A jack as claimed in claim 1; and a collar rotatably mounted on the post above the latch pin; and a cam surface on the collar rotatable with the collar to engage the lower end of the link and move it outward to cause the attached latch pin to move out of engagement with a recess.
 17. A jack as claimed in claim 16; and a notch in the lower edge of the collar engageable with the latch pin to prevent rotation of the collar; the notch being so located that when it is in locking engagement the cam surface is in non-lifting position with respect to the link.
 18. A jack as claimed in claim 1; and a collar slidably mounted on the post below the latch pin; an ear extending upward from the collar and formed with an aperture to slidingly receive the outer portion of the latch pin; the ear being located radially outward of the post a predetermined distance to limit outward movement of the link and disengagement of the latch pin from the slot.
 19. A jack as claimed in claim 18; and a coil spring surrounding the latch pin between the ear and the link to resiliently urge the link inward toward the post and cause the pin to enter the recess.
 20. A mechanical jack comprising: a ground engaging base; a hollow tubular support post mounted on the base in upright position; a pair of axially elongate guide slots extending through the wall of the post and arranged in parallel diametrically opposed relation; a hollow tubular load carrying column axially slidably mounted in the post to raise and lower a load and having a load engaging head at its upper end; two series of axially spaced apertures extending through the wall of the column for engagement by a lock pin and a latch pin, the two series being diametrically opposed and associated pairs of apertures being diametrically in register to define diametral passages through the column; a fulcrum fixedly mounted on thE post; an actuating lever pivotally mounted on the fulcrum for swinging about an axis transverse to the axis of the post and having a manual operating arm extending in a direction away from the post and a pair of actuating arms in parallel spaced relation and extending toward the post and passing on each side thereof; a pair of tension links, each pivotally connected at its upper end to the free end of one of the actuating arms and having a latch pin at its lower end resiliently biased to extend radially through one of the guide slots and into one of the apertures in the column; and a removable lock pin to engage an upper portion of the post and pass through an associated pair of apertures in the column to retain the column at a selected elevation with respect to the post; the inner ends of the latch pins being formed to positively engage the upper margins of associated apertures during upward movement of the pins and to be urged out of engagement by contact with lower margins of associated apertures during downward movement of the pins.
 21. A jack as claimed in claim 20; in which the lock pin projects out of the apertures at both sides of the column with its ends resting on the upper end of the post at diametrically opposite points to transmit the load from the column to the post. 